Netflix gives you the ability to rate, not just movies, but your favorite genres, too. You can indicate how much you love science fiction or hate romantic comedies. If you expand each genre by clicking on the plus sign to the left, you will see a bunch of subgenres. O'Grady's review mentioned the cool genres that Greencine has, but Netflix has plenty, too. For example, here's how the Action genre breaks down:
Comic Books and Superheroes
Military & War Action
I've discovered that rating genres has the effect of making my Netflix recommendations more accurate.